Low temperature photoconductivity of few layer p-type tungsten diselenide (WSe₂) field-effect transistors (FETs)

We report on the low-temperature photoconductive properties of few layer p-type tungsten diselenide (WSe₂) field-effect transistors (FETs) synthesized using the chemical vapor transport method. Photoconductivity measurements show that these FETs display room temperature photo-responsivities of ∼7 mAW^-1 when illuminated with a laser of wavelength λ = 658 nm with a power of 38 nW. The photo-responsivities of these FETs showed orders of magnitude improvement (up to ∼1.1 AW^-1 with external quantum efficiencies reaching as high as ∼188%) upon application of a gate voltage (V _G = -60 V). A temperature dependent (100 K < T < 300 K) photoconductivity study reveals a weak temperature dependence of responsivity for these WSe₂ phototransistors. We demonstrate that it is possible to obtain stable photo-responsivities of ∼0.76 ± 0.2 AW^-1 (with applied V _G = -60 V), at low temperatures in these FETs. These findings indicate the possibility of developing WSe₂-based FETs for highly robust, efficient, and swift photodetectors with a potential for optoelectronic applications over a broad range of temperatures.